This disclosure relates to the field of vibration damping and isolation. In particular, this disclosure relates to the provision of an active feedback path to enhance the isolation performance of a passive damping and isolation system.
In many applications, it is desirable to isolate sensitive equipment from the effects of vibration. The vibration energy may originate either through base motion transmission, as seen in dynamic vehicle applications, or through disturbances emanating on or near the isolated equipment, or both.
Passive isolation is the dominant existing solution for large system isolation, but suffers from the following shortcomings: (1) minimal low-frequency auto-alignment capability; (2) requirements of large clearance (sway space) around the isolator due to resonant amplification; (3) poor high-frequency isolation due to the fact that damping must be included to reduce the amount of requisite sway space; and (4) an inability to reduce the amplitude of isolation side disturbances
In a passive isolator, the amount of isolation is related to the available sway space and the amount of displacement allowable at resonance. This dictates the frequency and damping characteristics, effecting the transmission function. It also allows the isolator to displace under accelerations and rotations at frequencies below the isolator resonance (and at DC). This displacement of the isolator is not desirable in systems where nominal auto-alignment with respect to the aircraft is required, as in directed energy applications.
While passive isolators provide exceptional isolation at high frequency (above 2 times the resonant frequency), passive isolators amplify disturbances at low frequencies. This deficiency in passive isolators is due primarily to the resonant characteristics of the flexure components of the passive isolators. In addition, in passive isolators the frequency dependence of the vibration damping is not easily tailored, since tailoring the damping typically requires changing the stiffness elements and/or the damping fluid.
In contrast, active damping isolation systems provide desirable vibration damping at low frequencies, and the frequency dependence of the vibration damping and isolation transmissibility of active isolators can be easily tailored. However, active isolators are typically more complex, and are higher in weight than comparable passive isolators. In addition, active isolators require power for operation, and as such, become inoperable upon a power failure. Accordingly, the use of only active isolators may reduce reliability.
There is a need for improved damping isolation systems that provide desirable vibration damping at high and low frequencies.